Transportation of hydrogen atom and molecule through X12Y12 nano-cages

Hydrogen technology provides efficient, clean and environment friendly alternative to fossil fuel. A major challenge in use of hydrogen fuel is effective storage and release of hydrogen. Therefore, information regarding the barrier for encapsulation and decapsulation are very vital for understanding the phenomenon. A number of reports describe exo(endo)hedral binding of H₂ to inorganic X₁₂Y₁₂ fullerenes; however, the information regarding the barrier for en(de)capsulation are very scarce. In this study, the barriers for encapsulation and release of hydrogen atom and hydrogen molecule through X₁₂Y₁₂ nano-cages (where X = Al, B, Y = N, P) are studied. The translation of H/H₂ through the surface of nano-cages (permeability) is studied through density functional theory calculations with M05-2X method. The kinetic barriers for en(de)capsulation are obtained through scanning potential energy surface along the motion through hexagon of the nano-cage. The size of the nano-cage plays significant role in determining the barrier for en(de)capsulation. The relative stability of exohedral and endohedral complexes of H₂/H with X₁₂Y₁₂ nano-cages is obtained through binding energy calculations. Distortion energies are also calculated and the results show that encapsulation of H₂/H does not distort the nano-cage. Moreover, important minima along PES are also fully characterized. Electronic structures of nano-cages including HOMO–LUMO gap, TDOS, PDOS and excitation energies are analyzed. The H–L gap analysis shows that exohedral complexes have minimal effect on the electronic nature of the nano-cage whereas the endohedral complexes have marked effect on the H–L gap.